Railway signaling system



June 9, 1942. J. H; PELIKAN RAILWAY SIGNALING SYSTEM Filed June l5, 1940Hfs' ATTORNEY Patented June 9, 1942 2,286,006 RAILWAY sIGNALING SYSTEMJohn M. Pelikan, Pittsburgh, Pa., assignor to The Union Switch & SignalCompany, Swssvale, Pa., a corporation of Pennsylvania Application June15, 1940, Serial No. 340,792

2 Claims.

My invention relates to railway traiic controlling apparatus, and moreparticularly to approach locking apparatus for use in interlockingsystems for railroads to lock a track switch against operation undercertain conditions when a signal governing movement of traffic over theswitch is manually put to stop. The purpose of such locking is toprevent the operation of the switch when a train is approaching at suchspeed that it cannot be readily stopped without overrunning the signal,

Where a track stretch includes a track switch, as for example wherethere is a passing siding or a branch track, it is necessary to arrangethe switch control mechanism so that the switch can be moved only whenthere are no moving trains in the vicinity of the switch, and to insurethat before the switch is moved that the signals governing movement oftrains across the switch are displaying stop indications, and also thata signal distant from the switch is conditioned to display a restrictiveindication so that a train approaching the switch will be able to stopbefore reaching the switch.

It has heretofore been proposed to provide a line circuit controlled bytrack relays of an approach zone in the track stretch leading to theswitch to detect Whether a train is approaching the switch. It has alsobeen proposed to provide another line circuit leading from the distantsignal to the control tower or other point from which the switch iscontrolled to indicate whether the distant signal is displaying arestrictive indication.

The approach zone of the track stretch which must be checked foroccupancy is relatively long, while the distant signal which must bechecked is located a considerable distance from the track switch.Accordingly the line circuits for checking the distant signal andoccupancy of the approach zone of the track stretch are quite long andinstallation and maintenance of the wires for these line circuitsinvolves considerable eX- pense. Obviously there would be a substantialsaving if the same line circuit could be employed to check both thesignal and occupancy of the approach zone.

It is an object of this invention to provide imy proved equipment of thetype described which employs but a single line circuit to indicate atv aremote point the condition of a signal and of a stretch of railwaytrack.

A further object of the invention is to provide improved means employinga single line circuit CnA . -the novel features thereof in claims.

to indicate at a remote point the condition of a In the drawing Fig 1 isa diagram showing a stretch of railway track equipped with apparatusembodying my invention, and

Fig. 2 is a fragmentary view showing a modied form of apparatus which Imay employ in the system shown in Fig. 1.

Referring to the drawing, there is shown therein a stretch of railwaytrack having a main track A and a siding or diverging track B which .isconnected with the main track by means of a switch W. The switch W isoperated between its normal and reverse positions by a switch machine SMwhich may be of any suitable construction well-known in the art.

The main track A has track rails I and 2 which are divided by insulatedjoints 3 into the usual track sections, which are identified as sectionsI 0T and IIT which together constitute an approach zone, while adetector section 12T is provided and includes the switch W and theportions of the tracks A and B adjacent thereto.

Each of the track sections is provided with track circuit apparatuswhich may be of any well-known type. As shown each section has a trackbattery TB connected across the section rails adjacent one end of thesection, and a track relay TR having a winding connected across thesection rails adjacent the other end of the section.

The main track A is provided with wayside signals which govern movementof trains through the track stretch. Only the signals governing movementof trains from left to right have been shown, but it should beunderstood that other signals may be provided to govern movement oftrains from right to left if movement of trains in this direction iscontemplated.

The wayside signals may be of any suitable type and are here shown asbeing of the color Iight type.

The home signal at the switch W has an upper track A across the switch Wto the side or branch track B,

The signal SA has a green or clear lamp, a yellow or caution lamp, and ared or stop lamp, while the signal SB has a yellow or proceed lamp and ared or stop lamp.

A distance signal SD is located some distance from the switch W, thisdistance being such that trains traversing the track stretch andreceiving a restrictive indication at the signal SD will be able to stopbefore reaching the switch.

The signal SD has a green or clear lamp, a yellow or caution lamp, and ared or stop lamp.

The distant signal SD is controlled in any desired manner by traiiicconditions in advance of the signal so that the signal will display itsred or stop indication when a train is present in the track section HT.The signal SD is also controlled in accordance with the indicationdisplayed b-y the home signal SA, so that when the home signal isdisplaying its red or stop indication the signal SD will display itsyellow or caution indication.

The means by which the signal SD, is controlled in accordance withtraiiic conditions in advance, and by the indications displayed by thesignal SA is old and well-known in the art and has not been shown inorder to simplify the disclosure.

Similarly, the signal SA is controlled by trafc conditions in advance ofthe signal, while manually operated means is provided for at timesconditioning the signals SA and SB to display their red or stopindications, or to display proceed indications. The means by which thiscontrol of the signals is effected is old and wellknown in the art andhas not been shown in order to simplify the disclosure.

A polarized switch control relay WR, controls the switch machine SM inthe usual manner, while the supply of energy of normal or reversepolarity to the winding of the relay WR may be controlled in any mannerwell-known in the art.

The circuit of the winding of the switch control relay WR is controlledby an approach locking relay H, and by the track relay IZTR for thedetector section I2T. The circuit of the approach locking relay l-I iscontrolled by the relay G, and also by relay J, by a contact of therelay H, by the track relay IZTR, and by a contact of a time releasedevice, as hereinafter explained in detail.

A pair of line wires 20 and 2| coextensive with the section IIT areprovided, while energy is supplied over these wires for at timesenergizing the relays G and J. The means for supplying energy to theline wires comprises a coding device CT which has contacts 24 and 25which are continuously actuated between released and picked-up positionsby a motor or other suitable means. The contacts 24 and 25 control thecircuits for supplying energy from a battery 26 to the line wires, andare arranged so that when these contacts are picked up a circuit isestablished through which energy of one relative polarity, which may beconsidered to beof normal relative polarity, may be supplied to the linewires. When the contacts 24 and 25 are released a circuit isestablishedv through which energy of the opposite or re- Ashunting therelay winding.

verse polarity may be supplied from the battery 25 to the line wires 20and 2|.

The circuit for supplying energy of normal relative polarity to the linewires is controlled by contacts of the track relays IOTR and HTR so thatthe circuit is complete only when both of these relays are picked up.

The circuit for supplying energy of reverse relative polarity iscontrolled by contacts 29 and 39 which are governed in accordance withthe indication displayed by the distant signal SD. The contacts 29 and30 are controlled in such manner that they are picked up or closed whenand only when the signal SD is displaying its stop or cautionindication, and are released or open when the signal SD is displayingits clear indication.

Similarly, the circuit for supplying energy from the line wires 20 and2l to the winding of the relay G is controlled by a contact 34 which isgoverned in accordance with the indications displayed by the homesignals SA and SB in such manner that the contact is picked up when andonly when the signals SA and SB are both displaying stop indications,and is released when either of these signals is displaying a proceedindication.

The relays G and J are of the type employing a permanent magnet tomaintain the relay contacts in their released positions, and arearranged so that the relay contacts pick up only when energy of aparticular polarity is supplied to the relay winding. A relay of thetype which I may employ is shown in Letters Patent of the United StatesNo. 1,959,562, issued May 22, 1934, to Harry E. Ashworth. The relays Gand J are connected with the line wires so that the contact of the relayJ picks up only when impulses of energy of normal relative polarity aresupplied to the line wires, and so that the contact of the relay G picksup only when impulses of energy of reverse relative polarity aresupplied to the line wires.

The relays G and J ",each have associated therewith a rectier whichcontrols a circuit The rectier associated with each relay is connectedin such manner as to prevent ow of energy through the shunt circuit ofthe polarity intended to pick up the relay contact and to permit flow ofenergy of the opposite relative polarity. The arrangement of therectiers is such, therefore, that the winding of each relay is suppliedwith energy only of the polarity eective to pick up the relay contacts.As the relays G and J are of a type the contacts of which pick up onlywhen energy of a particular polarity is supplied to the relay winding,there is no possibility that the contacts of either of these relays willpick up if the shunt circuit for the relay is interrupted so that energyof the polarity other than that intended for the relay flows in therelay winding.

When the signal controlled contact 34 is released, it not onlyinterrupts the circuit of the winding of the relay G, but it alsoestablishes a circuit shunting the winding of the relay G so that energymay be supplied to the winding of the relay J. The circuit establishedin the released position of the contact 34 has a rectier 35 in seriestherewith and arranged to permit flow of energy of the polarity eiectiveto pick up the relay J and to prevent ilow of energy oi the oppositepolarity. Y

The equipment is shown in the condition which it assumes when there areno trains in the track stretch in the vicinity of the switch W, when theswitch W is in its normal position, and the signal SA is conditioned todisplay its `red or stop indication and the signal SD is displaying itsyellow or caution indication.

As it is assumed that the track stretch is vacant the track relays IUTR,I ITR and |2TR are energized by eurent supplied over the rails of thevarious track sections from the track batteries for these sections. Asthe track relays IUTR and l ITR are picked up impulses of energy ofnormal relative polarity are supplied over the line wires during thepicked-up periods of contacts 24 and 25 of the coding device CT toenergize the relay J and the contact 39 of this relay is picked up.

The circuit for supplying energy to the winding of the relay J is tracedfrom terminal B of the battery 26 through front contact 25 of the codingdevice CT, contact 3| of track relay |0TR, Contact 32 of track relayITR, line wire 2 l, front contact of the signal controlled contact 34,rectifier 45, winding of relay J, wire 20, contact 36 of track relay||TR, contact 38 of track relay |TR, and front contact 24 of the codingdevice CT to terminal C of the battery 26.

The circuit for supplying energy to the windingr of the relay J isinterrupted on movement of the contacts 24 and 25 of the coding deviceCT to their released positions. However, the relay J is rendered slow inreleasing by the rectiiier which is connected across the terminals ofthe relay winding, and, accordingly, the contact of this relay remainspicked up during the intervals between the supply of impulses of energyto the relay winding.

On movement of the contacts 24 and 25 of the coding device CT to theirreleased positions they engage their back points of contact, and energyof reverse relative polarity is supplied to the line wires as the signalcontrolled contacts 29 and 30 are picked up.

As pointed out above, the contacts 29 and 3|] are governed in accordancewith the aspect displayed by the distant signal SD in such manner thatthese contacts are picked up or closed when and only when the signal SDis displaying either its stop or its caution indication. As the signalSD is assumed to be displaying its caution indif cation the contacts 29and 30 are picked up and impulses of energy of reverse relative polarityare supplied to the line wires 20 and 2|.

In addition, as the signal SA is assumed to be displaying its stopindication the contact 34 is picked up and interrupts the circuit ofrelay G. Accordingly, the circuit for supplying impulses of energy ofreverse relative polarity to the relay G is complete and is traced fromterminal B of the battery 26 through back contact 25 of the codingdevice CT, front contact 3U, line wire 20, rectier 46 associated withrelay J, winding of relay G, front contact 34, line wire 2 I, frontcontact 29, and back contact 24 of the coding device CT to terminal C ofthe battery 26.

It will be seen, therefore, that when the signal SD displays its cautionindication the circuit for supplying impulses of energy of reverserelative polarity to the line Wires 2|) and 2| is complete, and that ifthe approach section remains unoccupied impulses of energy of normalrelative polarity continue to be supplied to the line wires. In additionit will be seen that when the home signals SA and SB are bothconditioned to display stop indications a circuit is established tosupply impulses of energy of reverse relative polarity from the linewires 20 and 2| to the relay G, while the circuit for supplying impulsesof energy of normal relative polarity of the relay J is maintained.

Accordingly, at this time the contact 39 of the relay J is picked up,while contact 40 of relay G is also picked up and the pick-up circuitfor supplying energy to the approach locking relay H is complete. Thecircuit is traced from terminal B of a local source of direct current,not shown, through front contact 40 of relay G, front contact 39 ofrelay J, and winding of relay H to terminal C of the source of current.

When relay H is picked up contact 48 establishes a stick circuit tomaintain the relay picked up as long as contact 40 of relay G remainspicked up.

In addition, when the approach locking relay H is picked up the circuitof the switch control relay WR is established, and the operator may movethe switch W to the reverse position by moving the switch control leverL to its reverse position to change the polarity of the current suppliedto the relay WR.

When the switch W attains its reverse position the operator maycondition the signal SB to display its proceed indication, and when thisis done contact 34 becomes released and interrupts the circuit forsupplying energy to the relay G and establishes a circuit including therectifier 35 for energizing the relay J.

Release of relay G releases the approach locking relay H, while releaseof the relay H interrupts the stick circuit for the relay, and inaddition, interrupts the circuit of the switch control relay WR toprevent movement of the switch W.

The system provided by this invention is arranged so that if a trainenters the approach zone at a time when one of the home signals isdisplaying a proceed indication, or the distant signal is displaying itsclear indication, the switch W will be locked, and cannot be movedexcept as hereinafter explained in detail.

When the distant signal SD is displaying its clear indication thecontacts 29 and 30 are released so that impulses of energy of reverserelative polarity are not supplied to the line wires 20 and 2|, whilewhen either one of the home signals is displaying a proceed indicationthe contact 34 is released and interrupts the circuit of the relay G sothat the contact 40 of the relay is released and interrupts the circuitof the approach locking relay H so that the contacts 42 and 43 of therelay H are released and interrupt the circuit of the switch controlrelay WR to prevent a change in the position of the switch W.

On entrance of a train into the section IUT the track relay |0TR.releases and interrupts the circuit for supplying impulses of energy ofnormal relative polarity to the line wires 20 and 2|. Accordingly,energy is no longer supplied to the relay J and the contact 39 of relayJ releases. When the train advances into section HTthe track relayII'I'R releases and additionally intere rupts the circuit for supplyingenergy of normal relative polarity to the line wires.

From the foregoing it will be seen that when a train enters the approachzone the supply of energy t0 pick up the relay J is cut 01T with theresult that the contact 39 becomes released to interrupt the pick-upcircuit for the approach locking relay H. The supply of energy to therelay J continues to be interrupted until the train vacates section IIT, and therefore the contact 39 of relay J remains released as long asthe train is present in the approach zone.

Accordingly, if after the train enters the approach zone the operatorplaces the home signals at stop so the Contact 34 becomes picked up andestablishes the circuit of the winding of the relay G with resultantpicking up of the contact 4t! of this relay, the circuit of the approachlocking relay H will not be established because contact 39 of relay J isreleased.

As the pick-up circuit of the relay H is not established this relayremains released and interrupts the circuit of the switch control relayWR to thereby prevent a change in the position of the switch W. This isdesirable as the train having received a clear indication at signal SDmay be traveling too fast to stop before reaching the switch W.

The system provided by this invention is arranged, however, so thatafter a train enters the approach zone the operator may change theposition of the switch W, but only after the eX- piration of apredetermined time interval subsequent to the time at which the homesignals are caused to display their stop indications. This time intervalis long enough to permit a train to stop before reaching the switch W,or to advance into the detector section I2T and thus release the trackrelay IZTR to thereby prevent a change in the position of the switch W.

As pointed out above when a train enters the approach Zone the trackrelay IUTR releases and interrupts the supply of energy to the relay Jso that the contact 39 of the relay J releases. If the home signals arenow both caused to display stop indications the contact 34 will pick up,while when the distant signal SD becomes conditioned to display arestrictive indication the contacts 29 and 30 will pick up with theresult that energy is supplied to the relay G and the contact 40 of thisrelay picks up. At this time, however, as contact 39 of relay J isreleased, the pick-up circuit of the approach locking relay H is notcomplete and the relay H remains released and continues to interrupt thecircuit of the switch control relay WR.

The operator may now establish a pick-up circuit for the approachlocking relay H by operating a time element device, not shown, whichcontrols a normally open contact 62. This device may be of any suitabledesign well-known in the art, as for example that shown in LettersPatent of the United States No. 2,114,895 to Harry E. Ashworth, and isarranged so that the contact 62 becomes closed only after the expirationof a predetermined time interval after operation of the device isinitiated. When contact 62 closes a circuit including contact 40 ofrelay G and the contact 62 is established to pick up the approachlocking relay H.

When relay H picks up its contact 48 establishes a stick circuit tomaintain the relay picked up as long as relay G is maintained picked up,while on picking up of relay H the circuit of the switch control relayWR is established, assuming that the train which had entered theapproach zone was able to stop before entering the detector section |2T.On establishment of the circuit of the switch control relay WR theoperator may move the switch W by changing the polarity of the currentsupplied to the relay WR, as eX- plained above.

When the switch W completes its movement the operator may condition theappropriate one of the home signals to display a proceed indication.When this is done contact 34 becomes released and interrupts the circuitfor supplying energy -to the relay G, and contact 40 becomes released tointerrupt the circuit of the approach locking relay H. Accordingly, therelay H releases and contact 48 interrupts the holding circuit for therelay winding, while contacts 42 and 43 interrupt the circuit of theswitch control relay to prevent further changes in the position of theswitch.

From the foregoing it will be seen that the system provided by thisinvention provides means requiring but a single line circuit toconstantly check the condition of the home and distant signals and ofoccupancy of an approach zone of track. It will be seen also that eachof these conditions is checked independently of the other with theresult that each may be determined irrespective of the other.

The condition of track occupancy is checked by the supply of impulses ofenergy of one relative polarity to the line circuit, while the supply ofthese impulses is controlled by the track relays of the approach zone insuch manner that the supply of these impulses is entirely independent oithe condition of the signals.

Similarly, the condition of the distant signal is checked by the supplyof impulses of energy of the other or reverse relative polarity to theline circuit, and the supply of these impulses of energy is entirelyindependent of the condition of occupancy of the approach zone.Likewise, the condition of the home signals is checked by the supply ofenergy of reverse relative polarity from the line circuit to the relayG, while the supply of energy to the relay G is independent of thecondition of occupancy of the track stretch.

In addition, the system is arranged so that impulses of energy of normalrelative polarity may be supplied from the line circuit to the relay Jregardless of the position of the signal controlled contact 3d.

It will be seen also that when the signal controlled contact 34 is inits released position and cuts off the supply of energy to the relay G,the circuit which is established to permit the supply of energy to therelay J includes a rectifier 35 in series therewith. The rectier 35permits flow of current of the polarity effective to pick up the relayJ, but prevents low of current of the opposite relative polarity in thiscircuit. This is advantageous as it prevents short circuiting of thebattery 26 if impulses of energy of reverse relative polarity aresupplied to the line circuit when the contact 34 is released.

The system shown in Fig. l of the drawing employs a coding device CT toprovide the alternate impulses of normal and reverse relative polarity.However, the invention is not limited to the use of this device, and ifalternating current is available this may be employed, and Fig. 2 isa'fragmentary View showing this modification.

Except as hereinafter specically pointed out in detail the modificationshown in Fig. 2 is the same as that shown in Fig. l, and the samereference characters are employed to identify the elements common toboth iigures.

In the modiiication shown in Fig. 2 a transformer TT is provided and hasits primary winding supplied with energy from a source of alternatingcurrent, the terminals of which are designated BX and CX.

One terminal of the secondary winding of the transformer TT is connectedwith contact 38 of the track relay IDTR, while the other terminal of thetransformer secondary winding is connected to contact 3| of the trackrelay IDTR. The circuits for connecting the transformer with thecontacts of the track relay include in series therewith asymmetric orrectifier units and 1I which are arranged to permit energy of normalrelative polarity to be supplied vto the line wires 2U and 2| and toprevent the supply of energy of the other or reverse relative polarityto the line wires.

In addition, one terminal of the transformer secondary winding isconnected with the signal controlled contact 29 and the other terminalof the transformer secondary winding is connected with the signalcontrolled contact 30. The circuits for connecting the transformersecondary winding with the signal controlled contacts include in seriestherewith asymmetric or rectier units 13 and `I4 which are arranged topermit energy of reverse relative polarity to be supplied to the linewires 2U and 2| and to prevent the supply of energy of the otherrelative polarity.

In operation, on the supply of alternating current energy to the primarywinding of the transformer TT impulses of energy of opposite relativepolarity are alternately induced in the secondary winding of thetransformer. If the contacts of the track relays ITR and IITR are pickedup impulses of energy of one or normal relative polarity induced in thetransformer secondary winding are supplied to the line circuit throughthe rectier units 1U and 1| and the track relay contacts.

Similarly, when the signal controlled contacts 29 and 3U are picked upimpulses of energy of reverse relative polarity are supplied from thetransformer to the line circuit through the rectifier units 13 and 14and the signal controlled contacts. l

Accordingly, if the signal controlled contacts and the track relaycontacts are both closed irnpulses of energy of each polarity will besupplied to the line circuit, the impulses of either polarity occurringduring the off periods between the supply of impulses of the otherrelative polarity.

Although I have herein shown and described only one form of railwaysignaling system embodying my invention, together with one modificationthereof which I may employ, it is understood that various changes andmodifications may be made therein within the scope of the appendedclaims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination, a stretch of railway track containing a switchmovable between a normal and a reverse position, an approach track zone,a distant signal governing movement of traic through said approach Zonetowards said switch, said distant signal being capable of displaying aclear indication and at least one restrictive indication, a home signalgoverning movement of trains across said switch, said home signal beingcapable of displaying a stop indication and at least one proceedindication, a pair of line conductors, means governed by said distantsignal and operative only when said signal is displaying a restrictiveindication to establish reverse supply connections to supply energy ofreverse relative polarity to said line conductors, means governed bytraiiic conditions in said approach zone CTI and operative only whensaid zone is vacant to establish normal supply connections to supplyenergy of normal relative polarity to said line conductors, means foralternately supplying iinpulses of energy to said normal and reversesupply connections, an approach locking relay operative when deenergizedto prevent movement of said switch, a first and a second control relayeach having a Winding included in series with the circuit of said lineconductors, each of said control relays having an asymmetric unitconnected across the relay winding to render the relay responsive toenergy of one polarity only and to also render the relay slow torelease, the unit associated with the first control relay being arrangedso that said relay is responsive to energy of reverse relative polarityonly and the unit associated with the second control relay beingarranged so that said relay is responsive to energy of normal polarityonly, a contact movable between a iirst and a second position, saidcontact being governed in accordance with the indication displayed bysaid home signal and occupying said rst position when and only when saidhome signal is displaying its stop indication, said contact beingoperable when occupying said first position to establish the circuit forconnecting the winding of the iirst control relay in series with saidline conductors, said contact being operable when occupying said secondposition to interrupt the circuit for connecting the winding of thefirst control relay in series with the line conductors and to connectthe line conductors in series with an asymmetric unit arranged to permitenergy of normal polarity only to iiow in said line conductors, wherebywhen said contact occupies said second position energy of normalpolarity may flow in the circuit of said line conductors and energizesaid second control relay but ilow of energy of reverse relativepolarity and resultant short circuiting of the source from which energyis supplied to said line conductors is prevented, a circuit completewhen the contacts of both of said control relays are picked up toenergize said approach locking relay, and a circuit for also energizingthe approach locking relay when the contacts of the second control relayare released provided the contacts of the rst control relay are pickedup.

2. In combination, a stretch of railway track containing a switchmovable between a normal and a reverse position, an approach track zone,a distant signal governing movement of traffic through said approachzone towards said switch, said distant signal being capable ofdisplaying a clear indication and at least one restrictive indication, ahome signal governing movement of trains across said switch, said homesignal being capable of displaying a stop indication and at least oneproceed indication, a pair of line conductors, means governed by saiddistant signal and operative only when said signal is displaying arestrictive indication to establish reverse supply connections to supplyenergy of reverse relative polarity to said line conductors, meansgoverned by traiiic conditions in said approach Zone and operative onlywhen said zone is vacant to establish normal supply connections tosupply energy of normal relative polarity to said line conductors, meansfor alternately supplying impulses of energy to said normal and reversesupply connections, an approach locking relay operative when deenergizedto prevent movement of said switch, acontact movable between a first anda second position, said contact being governed in accordance with theindication displayed by said home signal and occupying said firstposition when and only when said home signal is displaying its stopindication, a rst and a second control relay, the second control relayhaving a winding connected in series with said line conductors and alsoin series with asymmetric means arranged to permit energy of normal.polarity only to flow in said line conductors regardless of the positionof said signal controlled contact, an asymmetric. unit connected acrossthe terminals of the second control relay, said unit being arranged topermit energy of reverse relative polarity to flow therethrough, wherebyregardless of the position occupied` by said signal controlled Contactenergy of normal polarity supplied to said line conductors flows,through said asymmetric means and energizes said second control relay,said. signal controlled contact being effective when occupying its firstposition to connect the Winding of said first control relay in multiplewith said asymmetric means whereby when said signal controlled contactoccupies its rst position energy of reverse polarity supplied to saidline conductors flows through the asymmetric unit associated with saidsecond control relay and energizes the rst control relay, but when saidsignal controlled contact occupies its second position the circuit ofsaid rst control relay is interrupted and said asymmetric means preventsflow of energy of reverse polarity in saidv line conductors andresultant short circuiting of the source from which energy is suppliedto said line conductors, a circuit complete when the contacts of both ofsaid control relays are picked up to energize said approach lockingrelay, and a circuit for also energizing the approach relay when thecontacts of the second control relay are released provided the contactsof the first control relay are picked up.

JOHN M. PELIKAN.

